In moving transportations such as rotary-wing aircrafts and airplanes, symbol images on maneuvering information, mission information, etc., are provided as virtual images to a pilot by distantly displaying the symbol images superimposed with an external view. With this, the pilot can view the displayed contents (symbol images) at a true forward angle. As a result, the situation awareness can be improved, resulting in a reduced burden of maneuvering operations. In order to distantly display symbol images to the pilot as virtual images superimposed with the external scene, a head-up display apparatus (hereinafter also referred to as an “HUD apparatus”) has been used. The symbol images are distantly displayed by providing the light forming the symbol images with substantially parallel light rays so that the symbol images appear to the pilot as a distant “object” (e.g., with the same focal plane that a pilot might view an external object distant from the plane).
FIG. 6 is a side view showing a schematic structure of an aircraft cockpit (pilot compartment) equipped with a conventional HUD apparatus. In this disclosure, a direction horizontal (in this figure) to the ground and extending between the front and back of the aircraft or other vehicle is denoted as an X-direction, a direction horizontal to the ground and perpendicular to the X-direction is denoted as a Y-direction (a right-left direction with respect to aircraft/vehicle movement), and a direction perpendicular to the X-direction and the Y-direction is denoted as a Z-direction (up-down direction). The aircraft cockpit 101 is provided with a seat 12 to be occupied by a pilot P, a hemispherical glass windshield 11 surrounding the periphery of the head portion of the pilot P, instruments (not illustrated) arranged below and in front of the pilot P, and an HUD apparatus 120.
The instruments include a plurality of compact (e.g., 30 cm2) instrument panels. For example, a first instrument panel displays latitude information, a second instrument panel displays longitude information, and a third instrument panel displays altitude information. These instruments are arranged, for example, around the HUD apparatus 120.
The HUD apparatus 120 is provided with a combiner 21 arranged in front of a pilot P and a housing 130 arranged in lower front of the pilot P. The housing 130 houses an ultra-high luminance CRT 131 which creates symbol images, a collimating lens system 132, and a reflecting mirror 133. The combiner 21 is constituted by two plate-shaped members 21a and 21b each comprising a partial reflector to combine the light of received through the windshield 11 and light emitted from the collimating lens system 132. These two plate-shaped members 21a and 21b are arranged at a predetermined angle with respect to the Z-direction.
According to such HUD apparatus 120, the symbol image displayed on the ultra-high luminance CRT 131 is converted into approximately parallel light (which is equivalent to light rays Lo transmitted from a distance) via the collimating lens system 132 and the reflecting mirror 133, and reflected by the reflection plane of the combiner 21 to become symbol light Ls to viewable by the pilot P. The external light Lo transmitted through the windshield 11 and the combiner 21 is also viewable by the pilot P. Since the external light Lo is light from afar, the pilot P can simultaneously visually recognize both the external light Lo and the symbol light Ls without refocusing the eyes E.
However, aforementioned HUD apparatus 120 is large, and miniaturization is desirable, especially in a cockpit of an aircraft. As such, an HUD apparatus using a light guide in which a hologram is formed (for example, see JP-H07-502001 A), an HUD apparatus using a light guide in which a grating is formed (for example, see U.S. Pat. No. 4,711,512), an HUD apparatus using a light guide in which a polarization selective reflection film is formed (for example, see U.S. Application Publication 2012/0002256), etc., have been developed.
Additionally, a spectacles-type display has been developed (for example, see JP2003-536102). FIG. 7 is an external view showing a spectacles-type display to be worn by an observer, and FIG. 8 is an optical path diagram on an X-Y plane. The spectacles type display 150 has an appearance similar to spectacles, and includes a unit portion U that emits image display light Ls, a light guide 160 which is a plate member that leads the image display light Ls from the unit portion U to eyes E of an observer while reflecting the light inside, and a frame portion F to which the unit portion U and the light guide 160 are attached. The unit portion U includes a liquid crystal panel 171 and a collimating lens system (emission mechanism) 172.
The light guide 160 is, for example, a glass plane plate, and includes a planar mirror 161 formed at one end and arranged in front of the unit portion U, reflectors 162 formed at the other end and arranged in front of an eye E of an observer, and side planes 163 formed at the interface with the air and between the planar mirror 161 and the reflector 162. The side plane 163 is a rectangular shape as seen in the Y-direction, and includes a first plane 163a, a second plane 163b opposed to the first plane 163a in the X-direction, a third plane (not illustrated), and a fourth plane (not illustrated) opposed to the third plane in the Z-direction.
The reflectors 162 include a first reflector 162a of a planar shape, a second reflector 162b of a planar shape, and a third reflector 162c of a planar shape. In the −Y-direction, the first reflector 162a, the second reflector 162b, and the third reflector 162c are arranged in this order. Further, the first reflector 162a, the second reflector 162b, and the third reflector 162c are arranged so that the angle of the first reflector 162a with respect to the −Y-direction, the angle of the second reflector 162b with respect to the −Y-direction, and the angle of the third reflector 162c with respect to the −Y-direction are the same angle α (for example 24 degrees) as seen in the Z-direction. The first reflector 162a, the second reflector 162b, and the third reflector 162c each are not a plane having a reflectance of 1, but a beam splitter surface capable of partially reflecting the incident image display light Ls and partially transmitting the image display light Ls.
Such a light guide 160 is generally produced by laminating plate members each having a half mirror coated surface, cutting the laminated plate members in the oblique direction into a plate shape. It is known that the performance of the light guide 160 is decided by the parallelism of the reflectors 162a to 162c and the parallelism of the first plane 163a and the second plane 163b formed by cutting.
In the spectacles type display 150, the symbol image displayed on the liquid crystal panel is converted into approximately parallel light via the collimating lens system 172 and is incident to the light guide 160. After being reflected by the planar mirror 161, the symbol image travels as light rays in a zig-zag manner while being totally reflected by the first plane 163a and the second plane 163b. The light rays are partially reflected every time when incident to each of the reflectors 162a to 162c. When reached the first plane 163a, the light rays are taken out outside as parallel light rays since the total reflection condition is not satisfied and become visually recognizable by an observer.
Instruments provided in a conventional aircraft cockpit 101 are often constituted by a plurality of small instrument panels due to limitations of space. However, in recent years, a so-called “big-picture” configuration constituted by a single large display panel (display panel having a large area) is becoming popular, making space in the cockpit even more valuable and difficult to fit in equipment as desired. In an aircraft cockpit equipped with a “big-picture” display panel, use of a larger light guide (similar to 160 described above, but its size is, e.g., 20 cm+30 cm+2 cm) has been attempted. FIG. 3 is a side view showing a general structure of an aircraft cockpit equipped with an HUD apparatus using a light guide. The aircraft cockpit 201 is provided with a seat 12 to be occupied by a pilot P, a glass windshield 11 surrounding the periphery of a head portion of the pilot P, a display panel (instrument) 40 arranged in lower front of the pilot P, and an HUD apparatus (not illustrated).
The display panel 40 includes a display surface having a large area (e.g., 1,000 cm2) on which various information (e.g., latitude information and altitude information) is displayed. The display panel 40 is arranged on the rear wall of the housing 30. The display panel 40 may be arranged vertically.
As shown in FIG. 3, the light guide 260 is arranged at a position closer to the pilot P (−X-direction) so as to fit the light guide 260 into the cockpit in view of the space constraints imposed by the glass windshield 11. As shown in FIG. 3, arranging the light guide 260 in this fashion causes the light guide panel 260 to obstruct the view of the display panel 40 by the pilot P.
When arranging the light guide 360 so as not to be arranged to obstruct the view of the display panel 40, the windshield or other portions of the cockpit interfere with positioning the light guide 360 as shown in FIG. 4. If the light guide 360 is reduced in size to avoid contact with the windshield 11, the visual angle θ of the light guide 360 as seen from the pilot P (the instantaneous field of view or IFOV) decreases. In order to avoid the interference of a larger light guide with the windshield while still avoiding obstruction of the display 40, one may consider inclining the light guide 460 as shown by FIG. 5. However, in order to incline the light guide 460, it is required to reduce the inclination angle a of the reflector in the light guide 460, which causes cracks in the reflector during the manufacturing process.